Cylindrical Magnet Cavity for Position Sensor Volume Reduction
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Solution Overview
Problem
Current contactless magnetic position sensors face challenges in reducing size without sacrificing performance, particularly in achieving a low average magnetic induction close to 0 Gauss, which affects sensitivity and accuracy, especially when the distance between the sensor and the target increases.
Innovation Solution
A magnetic sensor design featuring a U-shaped or cylindrical permanent magnet with a cavity and a truncated conical ferromagnetic part, where the magneto-sensitive element is positioned to measure the axial component of the magnetic field near the narrowest part of the cone, allowing for reduced sensor size and volume while maintaining high performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the sensor size is reduced, then the manufacturing cost and complexity are decreased, but the sensitivity and measurement precision deteriorate
Solution Approach 1:
The patent applies local quality by creating a specific geometric configuration where the conical ferromagnetic target and cylindrical permanent magnet form a localized high-gradient magnetic field region. The cone angle (15-45 degrees) and magnet dimensions are optimized to concentrate magnetic flux in a specific spatial location, achieving high sensitivity in a compact volume without requiring the entire sensor to be large.
Solution Approach 2:
The patent transitions from planar magnet arrangements to a three-dimensional configuration with the conical target positioned within the cylindrical magnet's magnetic field. This spatial arrangement in multiple dimensions creates a more efficient use of magnetic flux and enables higher measurement precision in a reduced volume by exploiting the z-axis dimension for field gradient optimization.
2Adaptability or versatility
If the distance between the magneto-sensitive element and the target is increased, then the air gap tolerance is improved, but the magnetic induction variation and sensitivity decrease
Solution Approach 1:
The patent utilizes parameter changes by varying the cone angle (15-45 degrees) and the relative dimensions of the conical target and cylindrical magnet to optimize the magnetic field gradient characteristics. By adjusting these geometric parameters, the system achieves a balance where sufficient field variation is maintained even with increased air gap, improving tolerance while preserving sensitivity.
Solution Approach 2:
The patent implements dynamics by designing a magnetic field configuration that adapts to varying air gap conditions. The conical geometry creates a progressive field gradient that maintains measurement capability across a range of distances, allowing the sensor to dynamically respond to different target positions while maintaining precision.
3Measurement precision
If a cavity is created in the permanent magnet to reduce average induction, then the sensitivity is improved, but the manufacturing complexity and volume increase
Solution Approach 1:
The patent applies the taking out principle by removing material from the center of the cylindrical permanent magnet to create a cavity that accommodates the conical ferromagnetic target. This extraction reduces the average magnetic induction at the magneto-sensitive element location by eliminating magnet material that would otherwise contribute to background field, thereby improving signal-to-noise ratio while maintaining a relatively simple cylindrical outer structure.
4Measurement precision
If multiple magneto-sensitive elements are used to cancel average induction, then the measurement precision is improved, but the device complexity and cost increase
Solution Approach 1:
The patent removes the need for multiple magneto-sensitive elements by taking out (extracting) the source of average induction through the cavity design. By creating a cavity in the permanent magnet, the system achieves low average induction with a single element, eliminating the complexity and cost of multiple elements while maintaining measurement precision.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design enables the detection of position information as soon as the sensor is powered, with improved sensitivity and accuracy, allowing for a larger target-magnet air gap while maintaining high performance and reducing manufacturing costs.
Implementation Method 1
a permanent magnet (1) magnetized substantially in the axial direction
Implementation Method 2
measuring the axial component of the magnetic field
Implementation Method 3
the variation of induction generated by the variation of reluctance between a ferromagnetic part and a permanent magnet
Implementation Method 4
A Hall effect probe placed above this assembly, between the target and the magnet, measures the variation of the magnetic induction
Data Source
Figure 1a~1d
Figure 2~4
Figure 5~7
AI summary
The invention relates to a contactless magnetic sensor for measuring the angular or linear movement of a ferromagnetic target. The purpose of the invention is to make a position sensor having reduced dimensions and capable of detecting a piece of position information as soon as the sensor is powered without degrading the performance thereof. To this end, the invention relates to a mobile sensor (4) that comprises at least one permanent magnet (1), at least one ferromagnetic member (2) at least one magnetically sensitive member (3), the permanent magnet having an upper surface opposite the ferromagnetic target (4), wherein the permanent magnet has a substantially cylindrical or parallelepiped shape and comprises a cavity (5), the ferromagnetic member (2) being arranged inside the cavity (5) and the magnetically sensitive member being arranged inside the cavity (5) above the ferromagnetic member (2) and below the upper surface of the magnet (1).